could somebody pleas explain exatly what Poke-sav is?

thank you much abliged

All I know is that its a computer program that creates hacked pokemon. You get the pokemon through Action Replay, from what I have heard it has the ability to make legit looking pokemon, from my experience that is true because I got a shiny event mew that looked legit before I learned you can NOT obtain a legit event mew... I had sad face all over.

its a prowhere u can change the ot, id etc

Pokesav is a program for generating any Pokemon you want to be pretty much however you want. EV's, attacks, Nature, etc. Once you have designed the Pokemon you want, it finalizes the creation of it with an Action Replay code that you will use on your game to have it be generated in your PC.
While it's true that they can look very legit, and short of mimicking Event Pokemon, they can technically be truly no different, done correctly, usually people will indulge themselves in making some 'extra' feature to the Pokemon (Say, giving the Pokemon Wonder Guard, or an attack it couldn't possibly learn, such as a Venasaur with Fly) or miss something that would make it the same as if they'd gotten it properly.

I've never used it myself, and personally have no interest in doing so. This information is what I've gathered from other sites.

Though, I do have to admit, I'd possibly be tempted to use it if there was a version of Pokesav for Pokemon B/W that spawned the Pokemon in the Dream World Forest in the game, so it could even be caught properly, and in any ball deisired, as well as having their Dream World Ability. (You CAN mod with Pokesav for any ball, but there are some pokemon that, outside of them being sent to that forest, CAN'T legally be in other balls; such as Event's are always in Cherish Balls, Starter Pokemon are always in Pokeballs (Since they can only be given or bred, both in Pokeball))

I've heard that it is like a Gameshark. Although I am not completly sure.

I also heard its like gameshark but i never tried it, should i?

DIRTEE ROTTEN CHEATIN

It's a program (or rather, a series of programs made for each different game) that modifies a save file for the DS games, most feasibly when you're playing a ROM by some means other than on a real DS cartridge. You can change whatever. The species of a Pokémon, its moves, the PP it has for moves, its stats, its gender, whether it's shiny or not, where it was caught, what ball it is in, what the player and rival's names are, where you are standing, what items you have, how complete your Pokédex is.

Everything.

I use it for good instead of evil. Looking at and comparing IVs (not changing them) instead of using unreliable calculators and things, changing nicknames of Pokémon I got in trades or from my other games.